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                    浮点数
            
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                    方法
            
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                    方法值和方法表达式
            
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                    示例: Bit数组
            
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                    封装
            
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                    接口
            
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                    接口是合约
            
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                    接口类型
            
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                    实现接口的条件
            
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                    flag.Value接口
            
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                    接口值
            
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                    sort.Interface接口
            
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                    http.Handler接口
            
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                    error接口
            
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                    示例: 表达式求值
            
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                    类型断言
            
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                    基于类型断言识别错误类型
            
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                    通过类型断言查询接口
            
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                    类型分支
            
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                    示例: 基于标记的XML解码
            
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                    补充几点
            
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                    Goroutines和Channels
            
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                    Goroutines
            
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                    示例: 并发的Clock服务
            
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                    示例: 并发的Echo服务
            
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                    Channels
            
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                    并发的循环
            
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                    示例: 并发的Web爬虫
            
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                    基于select的多路复用
            
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                    示例: 并发的目录遍历
            
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                    并发的退出
            
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                    示例: 聊天服务
            
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        <li class="chapter " data-level="1.10" data-path="../ch9/ch9.html">
            
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                    基于共享变量的并发
            
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                    竞争条件
            
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                    sync.Mutex互斥锁
            
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                    sync.RWMutex读写锁
            
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                    内存同步
            
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                    sync.Once惰性初始化
            
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        <li class="chapter " data-level="1.10.6" data-path="../ch9/ch9-06.html">
            
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                    竞争条件检测
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.7" data-path="../ch9/ch9-07.html">
            
                <a href="../ch9/ch9-07.html">
            
                    
                    示例: 并发的非阻塞缓存
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.10.8" data-path="../ch9/ch9-08.html">
            
                <a href="../ch9/ch9-08.html">
            
                    
                    Goroutines和线程
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.11" data-path="../ch10/ch10.html">
            
                <a href="../ch10/ch10.html">
            
                    
                    包和工具
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.11.1" data-path="../ch10/ch10-01.html">
            
                <a href="../ch10/ch10-01.html">
            
                    
                    包简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.2" data-path="../ch10/ch10-02.html">
            
                <a href="../ch10/ch10-02.html">
            
                    
                    导入路径
            
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        <li class="chapter " data-level="1.11.3" data-path="../ch10/ch10-03.html">
            
                <a href="../ch10/ch10-03.html">
            
                    
                    包声明
            
                </a>
            

            
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        <li class="chapter " data-level="1.11.4" data-path="../ch10/ch10-04.html">
            
                <a href="../ch10/ch10-04.html">
            
                    
                    导入声明
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.5" data-path="../ch10/ch10-05.html">
            
                <a href="../ch10/ch10-05.html">
            
                    
                    包的匿名导入
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.6" data-path="../ch10/ch10-06.html">
            
                <a href="../ch10/ch10-06.html">
            
                    
                    包和命名
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.11.7" data-path="../ch10/ch10-07.html">
            
                <a href="../ch10/ch10-07.html">
            
                    
                    工具
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.12" data-path="../ch11/ch11.html">
            
                <a href="../ch11/ch11.html">
            
                    
                    测试
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.12.1" data-path="../ch11/ch11-01.html">
            
                <a href="../ch11/ch11-01.html">
            
                    
                    go test
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.2" data-path="../ch11/ch11-02.html">
            
                <a href="../ch11/ch11-02.html">
            
                    
                    测试函数
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.3" data-path="../ch11/ch11-03.html">
            
                <a href="../ch11/ch11-03.html">
            
                    
                    测试覆盖率
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.4" data-path="../ch11/ch11-04.html">
            
                <a href="../ch11/ch11-04.html">
            
                    
                    基准测试
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.5" data-path="../ch11/ch11-05.html">
            
                <a href="../ch11/ch11-05.html">
            
                    
                    剖析
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.12.6" data-path="../ch11/ch11-06.html">
            
                <a href="../ch11/ch11-06.html">
            
                    
                    示例函数
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.13" data-path="../ch12/ch12.html">
            
                <a href="../ch12/ch12.html">
            
                    
                    反射
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.13.1" data-path="../ch12/ch12-01.html">
            
                <a href="../ch12/ch12-01.html">
            
                    
                    为何需要反射?
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.2" data-path="../ch12/ch12-02.html">
            
                <a href="../ch12/ch12-02.html">
            
                    
                    reflect.Type和reflect.Value
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.3" data-path="../ch12/ch12-03.html">
            
                <a href="../ch12/ch12-03.html">
            
                    
                    Display递归打印
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.4" data-path="../ch12/ch12-04.html">
            
                <a href="../ch12/ch12-04.html">
            
                    
                    示例: 编码S表达式
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.5" data-path="../ch12/ch12-05.html">
            
                <a href="../ch12/ch12-05.html">
            
                    
                    通过reflect.Value修改值
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.6" data-path="../ch12/ch12-06.html">
            
                <a href="../ch12/ch12-06.html">
            
                    
                    示例: 解码S表达式
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.7" data-path="../ch12/ch12-07.html">
            
                <a href="../ch12/ch12-07.html">
            
                    
                    获取结构体字段标签
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.8" data-path="../ch12/ch12-08.html">
            
                <a href="../ch12/ch12-08.html">
            
                    
                    显示一个类型的方法集
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.13.9" data-path="../ch12/ch12-09.html">
            
                <a href="../ch12/ch12-09.html">
            
                    
                    几点忠告
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="1.14" data-path="../ch13/ch13.html">
            
                <a href="../ch13/ch13.html">
            
                    
                    底层编程
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.14.1" data-path="../ch13/ch13-01.html">
            
                <a href="../ch13/ch13-01.html">
            
                    
                    unsafe.Sizeof, Alignof 和 Offsetof
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.2" data-path="../ch13/ch13-02.html">
            
                <a href="../ch13/ch13-02.html">
            
                    
                    unsafe.Pointer
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.3" data-path="../ch13/ch13-03.html">
            
                <a href="../ch13/ch13-03.html">
            
                    
                    示例: 深度相等判断
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.4" data-path="../ch13/ch13-04.html">
            
                <a href="../ch13/ch13-04.html">
            
                    
                    通过cgo调用C代码
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.14.5" data-path="../ch13/ch13-05.html">
            
                <a href="../ch13/ch13-05.html">
            
                    
                    几点忠告
            
                </a>
            

            
        </li>
    

            </ul>
            
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        <li class="chapter " data-level="1.15" data-path="../appendix/appendix.html">
            
                <a href="../appendix/appendix.html">
            
                    
                    附录
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="1.15.1" data-path="../appendix/appendix-a-errata.html">
            
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                    附录A：原文勘误
            
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                    附录B：作者译者
            
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                    附录C：译文授权
            
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        <li class="chapter " data-level="1.15.4" data-path="../appendix/appendix-d-translations.html">
            
                <a href="../appendix/appendix-d-translations.html">
            
                    
                    附录D：其它语言
            
                </a>
            

            
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                                <h2 id="32-&#x6D6E;&#x70B9;&#x6570;">3.2. &#x6D6E;&#x70B9;&#x6570;</h2>
<p>Go&#x8BED;&#x8A00;&#x63D0;&#x4F9B;&#x4E86;&#x4E24;&#x79CD;&#x7CBE;&#x5EA6;&#x7684;&#x6D6E;&#x70B9;&#x6570;&#xFF0C;float32&#x548C;float64&#x3002;&#x5B83;&#x4EEC;&#x7684;&#x7B97;&#x672F;&#x89C4;&#x8303;&#x7531;IEEE754&#x6D6E;&#x70B9;&#x6570;&#x56FD;&#x9645;&#x6807;&#x51C6;&#x5B9A;&#x4E49;&#xFF0C;&#x8BE5;&#x6D6E;&#x70B9;&#x6570;&#x89C4;&#x8303;&#x88AB;&#x6240;&#x6709;&#x73B0;&#x4EE3;&#x7684;CPU&#x652F;&#x6301;&#x3002;</p>
<p>&#x8FD9;&#x4E9B;&#x6D6E;&#x70B9;&#x6570;&#x7C7B;&#x578B;&#x7684;&#x53D6;&#x503C;&#x8303;&#x56F4;&#x53EF;&#x4EE5;&#x4ECE;&#x5F88;&#x5FAE;&#x5C0F;&#x5230;&#x5F88;&#x5DE8;&#x5927;&#x3002;&#x6D6E;&#x70B9;&#x6570;&#x7684;&#x8303;&#x56F4;&#x6781;&#x9650;&#x503C;&#x53EF;&#x4EE5;&#x5728;math&#x5305;&#x627E;&#x5230;&#x3002;&#x5E38;&#x91CF;math.MaxFloat32&#x8868;&#x793A;float32&#x80FD;&#x8868;&#x793A;&#x7684;&#x6700;&#x5927;&#x6570;&#x503C;&#xFF0C;&#x5927;&#x7EA6;&#x662F; 3.4e38&#xFF1B;&#x5BF9;&#x5E94;&#x7684;math.MaxFloat64&#x5E38;&#x91CF;&#x5927;&#x7EA6;&#x662F;1.8e308&#x3002;&#x5B83;&#x4EEC;&#x5206;&#x522B;&#x80FD;&#x8868;&#x793A;&#x7684;&#x6700;&#x5C0F;&#x503C;&#x8FD1;&#x4F3C;&#x4E3A;1.4e-45&#x548C;4.9e-324&#x3002;</p>
<p>&#x4E00;&#x4E2A;float32&#x7C7B;&#x578B;&#x7684;&#x6D6E;&#x70B9;&#x6570;&#x53EF;&#x4EE5;&#x63D0;&#x4F9B;&#x5927;&#x7EA6;6&#x4E2A;&#x5341;&#x8FDB;&#x5236;&#x6570;&#x7684;&#x7CBE;&#x5EA6;&#xFF0C;&#x800C;float64&#x5219;&#x53EF;&#x4EE5;&#x63D0;&#x4F9B;&#x7EA6;15&#x4E2A;&#x5341;&#x8FDB;&#x5236;&#x6570;&#x7684;&#x7CBE;&#x5EA6;&#xFF1B;&#x901A;&#x5E38;&#x5E94;&#x8BE5;&#x4F18;&#x5148;&#x4F7F;&#x7528;float64&#x7C7B;&#x578B;&#xFF0C;&#x56E0;&#x4E3A;float32&#x7C7B;&#x578B;&#x7684;&#x7D2F;&#x8BA1;&#x8BA1;&#x7B97;&#x8BEF;&#x5DEE;&#x5F88;&#x5BB9;&#x6613;&#x6269;&#x6563;&#xFF0C;&#x5E76;&#x4E14;float32&#x80FD;&#x7CBE;&#x786E;&#x8868;&#x793A;&#x7684;&#x6B63;&#x6574;&#x6570;&#x5E76;&#x4E0D;&#x662F;&#x5F88;&#x5927;&#xFF08;&#x8BD1;&#x6CE8;&#xFF1A;&#x56E0;&#x4E3A;float32&#x7684;&#x6709;&#x6548;bit&#x4F4D;&#x53EA;&#x6709;23&#x4E2A;&#xFF0C;&#x5176;&#x5B83;&#x7684;bit&#x4F4D;&#x7528;&#x4E8E;&#x6307;&#x6570;&#x548C;&#x7B26;&#x53F7;&#xFF1B;&#x5F53;&#x6574;&#x6570;&#x5927;&#x4E8E;23bit&#x80FD;&#x8868;&#x8FBE;&#x7684;&#x8303;&#x56F4;&#x65F6;&#xFF0C;float32&#x7684;&#x8868;&#x793A;&#x5C06;&#x51FA;&#x73B0;&#x8BEF;&#x5DEE;&#xFF09;&#xFF1A;</p>
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> f <span class="hljs-keyword">float32</span> = <span class="hljs-number">16777216</span> <span class="hljs-comment">// 1 &lt;&lt; 24</span>
fmt.Println(f == f+<span class="hljs-number">1</span>)    <span class="hljs-comment">// &quot;true&quot;!</span>
</code></pre>
<p>&#x6D6E;&#x70B9;&#x6570;&#x7684;&#x5B57;&#x9762;&#x503C;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x5199;&#x5C0F;&#x6570;&#x90E8;&#x5206;&#xFF0C;&#x50CF;&#x8FD9;&#x6837;&#xFF1A;</p>
<pre><code class="lang-Go"><span class="hljs-keyword">const</span> e = <span class="hljs-number">2.71828</span> <span class="hljs-comment">// (approximately)</span>
</code></pre>
<p>&#x5C0F;&#x6570;&#x70B9;&#x524D;&#x9762;&#x6216;&#x540E;&#x9762;&#x7684;&#x6570;&#x5B57;&#x90FD;&#x53EF;&#x80FD;&#x88AB;&#x7701;&#x7565;&#xFF08;&#x4F8B;&#x5982;.707&#x6216;1.&#xFF09;&#x3002;&#x5F88;&#x5C0F;&#x6216;&#x5F88;&#x5927;&#x7684;&#x6570;&#x6700;&#x597D;&#x7528;&#x79D1;&#x5B66;&#x8BA1;&#x6570;&#x6CD5;&#x4E66;&#x5199;&#xFF0C;&#x901A;&#x8FC7;e&#x6216;E&#x6765;&#x6307;&#x5B9A;&#x6307;&#x6570;&#x90E8;&#x5206;&#xFF1A;</p>
<pre><code class="lang-Go"><span class="hljs-keyword">const</span> Avogadro = <span class="hljs-number">6.02214129e23</span>  <span class="hljs-comment">// &#x963F;&#x4F0F;&#x4F3D;&#x5FB7;&#x7F57;&#x5E38;&#x6570;</span>
<span class="hljs-keyword">const</span> Planck   = <span class="hljs-number">6.62606957e-34</span> <span class="hljs-comment">// &#x666E;&#x6717;&#x514B;&#x5E38;&#x6570;</span>
</code></pre>
<p>&#x7528;Printf&#x51FD;&#x6570;&#x7684;%g&#x53C2;&#x6570;&#x6253;&#x5370;&#x6D6E;&#x70B9;&#x6570;&#xFF0C;&#x5C06;&#x91C7;&#x7528;&#x66F4;&#x7D27;&#x51D1;&#x7684;&#x8868;&#x793A;&#x5F62;&#x5F0F;&#x6253;&#x5370;&#xFF0C;&#x5E76;&#x63D0;&#x4F9B;&#x8DB3;&#x591F;&#x7684;&#x7CBE;&#x5EA6;&#xFF0C;&#x4F46;&#x662F;&#x5BF9;&#x5E94;&#x8868;&#x683C;&#x7684;&#x6570;&#x636E;&#xFF0C;&#x4F7F;&#x7528;%e&#xFF08;&#x5E26;&#x6307;&#x6570;&#xFF09;&#x6216;%f&#x7684;&#x5F62;&#x5F0F;&#x6253;&#x5370;&#x53EF;&#x80FD;&#x66F4;&#x5408;&#x9002;&#x3002;&#x6240;&#x6709;&#x7684;&#x8FD9;&#x4E09;&#x4E2A;&#x6253;&#x5370;&#x5F62;&#x5F0F;&#x90FD;&#x53EF;&#x4EE5;&#x6307;&#x5B9A;&#x6253;&#x5370;&#x7684;&#x5BBD;&#x5EA6;&#x548C;&#x63A7;&#x5236;&#x6253;&#x5370;&#x7CBE;&#x5EA6;&#x3002;</p>
<pre><code class="lang-Go"><span class="hljs-keyword">for</span> x := <span class="hljs-number">0</span>; x &lt; <span class="hljs-number">8</span>; x++ {
    fmt.Printf(<span class="hljs-string">&quot;x = %d e^x = %8.3f\n&quot;</span>, x, math.Exp(<span class="hljs-keyword">float64</span>(x)))
}
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x6253;&#x5370;e&#x7684;&#x5E42;&#xFF0C;&#x6253;&#x5370;&#x7CBE;&#x5EA6;&#x662F;&#x5C0F;&#x6570;&#x70B9;&#x540E;&#x4E09;&#x4E2A;&#x5C0F;&#x6570;&#x7CBE;&#x5EA6;&#x548C;8&#x4E2A;&#x5B57;&#x7B26;&#x5BBD;&#x5EA6;&#xFF1A;</p>
<pre><code>x = 0       e^x =    1.000
x = 1       e^x =    2.718
x = 2       e^x =    7.389
x = 3       e^x =   20.086
x = 4       e^x =   54.598
x = 5       e^x =  148.413
x = 6       e^x =  403.429
x = 7       e^x = 1096.633
</code></pre><p>math&#x5305;&#x4E2D;&#x9664;&#x4E86;&#x63D0;&#x4F9B;&#x5927;&#x91CF;&#x5E38;&#x7528;&#x7684;&#x6570;&#x5B66;&#x51FD;&#x6570;&#x5916;&#xFF0C;&#x8FD8;&#x63D0;&#x4F9B;&#x4E86;IEEE754&#x6D6E;&#x70B9;&#x6570;&#x6807;&#x51C6;&#x4E2D;&#x5B9A;&#x4E49;&#x7684;&#x7279;&#x6B8A;&#x503C;&#x7684;&#x521B;&#x5EFA;&#x548C;&#x6D4B;&#x8BD5;&#xFF1A;&#x6B63;&#x65E0;&#x7A77;&#x5927;&#x548C;&#x8D1F;&#x65E0;&#x7A77;&#x5927;&#xFF0C;&#x5206;&#x522B;&#x7528;&#x4E8E;&#x8868;&#x793A;&#x592A;&#x5927;&#x6EA2;&#x51FA;&#x7684;&#x6570;&#x5B57;&#x548C;&#x9664;&#x96F6;&#x7684;&#x7ED3;&#x679C;&#xFF1B;&#x8FD8;&#x6709;NaN&#x975E;&#x6570;&#xFF0C;&#x4E00;&#x822C;&#x7528;&#x4E8E;&#x8868;&#x793A;&#x65E0;&#x6548;&#x7684;&#x9664;&#x6CD5;&#x64CD;&#x4F5C;&#x7ED3;&#x679C;0/0&#x6216;Sqrt(-1).</p>
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> z <span class="hljs-keyword">float64</span>
fmt.Println(z, -z, <span class="hljs-number">1</span>/z, <span class="hljs-number">-1</span>/z, z/z) <span class="hljs-comment">// &quot;0 -0 +Inf -Inf NaN&quot;</span>
</code></pre>
<p>&#x51FD;&#x6570;math.IsNaN&#x7528;&#x4E8E;&#x6D4B;&#x8BD5;&#x4E00;&#x4E2A;&#x6570;&#x662F;&#x5426;&#x662F;&#x975E;&#x6570;NaN&#xFF0C;math.NaN&#x5219;&#x8FD4;&#x56DE;&#x975E;&#x6570;&#x5BF9;&#x5E94;&#x7684;&#x503C;&#x3002;&#x867D;&#x7136;&#x53EF;&#x4EE5;&#x7528;math.NaN&#x6765;&#x8868;&#x793A;&#x4E00;&#x4E2A;&#x975E;&#x6CD5;&#x7684;&#x7ED3;&#x679C;&#xFF0C;&#x4F46;&#x662F;&#x6D4B;&#x8BD5;&#x4E00;&#x4E2A;&#x7ED3;&#x679C;&#x662F;&#x5426;&#x662F;&#x975E;&#x6570;NaN&#x5219;&#x662F;&#x5145;&#x6EE1;&#x98CE;&#x9669;&#x7684;&#xFF0C;&#x56E0;&#x4E3A;NaN&#x548C;&#x4EFB;&#x4F55;&#x6570;&#x90FD;&#x662F;&#x4E0D;&#x76F8;&#x7B49;&#x7684;&#xFF08;&#x8BD1;&#x6CE8;&#xFF1A;&#x5728;&#x6D6E;&#x70B9;&#x6570;&#x4E2D;&#xFF0C;NaN&#x3001;&#x6B63;&#x65E0;&#x7A77;&#x5927;&#x548C;&#x8D1F;&#x65E0;&#x7A77;&#x5927;&#x90FD;&#x4E0D;&#x662F;&#x552F;&#x4E00;&#x7684;&#xFF0C;&#x6BCF;&#x4E2A;&#x90FD;&#x6709;&#x975E;&#x5E38;&#x591A;&#x79CD;&#x7684;bit&#x6A21;&#x5F0F;&#x8868;&#x793A;&#xFF09;&#xFF1A;</p>
<pre><code class="lang-Go">nan := math.NaN()
fmt.Println(nan == nan, nan &lt; nan, nan &gt; nan) <span class="hljs-comment">// &quot;false false false&quot;</span>
</code></pre>
<p>&#x5982;&#x679C;&#x4E00;&#x4E2A;&#x51FD;&#x6570;&#x8FD4;&#x56DE;&#x7684;&#x6D6E;&#x70B9;&#x6570;&#x7ED3;&#x679C;&#x53EF;&#x80FD;&#x5931;&#x8D25;&#xFF0C;&#x6700;&#x597D;&#x7684;&#x505A;&#x6CD5;&#x662F;&#x7528;&#x5355;&#x72EC;&#x7684;&#x6807;&#x5FD7;&#x62A5;&#x544A;&#x5931;&#x8D25;&#xFF0C;&#x50CF;&#x8FD9;&#x6837;&#xFF1A;</p>
<pre><code class="lang-Go"><span class="hljs-keyword">func</span> compute() (value <span class="hljs-keyword">float64</span>, ok <span class="hljs-keyword">bool</span>) {
    <span class="hljs-comment">// ...</span>
    <span class="hljs-keyword">if</span> failed {
        <span class="hljs-keyword">return</span> <span class="hljs-number">0</span>, <span class="hljs-literal">false</span>
    }
    <span class="hljs-keyword">return</span> result, <span class="hljs-literal">true</span>
}
</code></pre>
<p>&#x63A5;&#x4E0B;&#x6765;&#x7684;&#x7A0B;&#x5E8F;&#x6F14;&#x793A;&#x4E86;&#x901A;&#x8FC7;&#x6D6E;&#x70B9;&#x8BA1;&#x7B97;&#x751F;&#x6210;&#x7684;&#x56FE;&#x5F62;&#x3002;&#x5B83;&#x662F;&#x5E26;&#x6709;&#x4E24;&#x4E2A;&#x53C2;&#x6570;&#x7684;z = f(x, y)&#x51FD;&#x6570;&#x7684;&#x4E09;&#x7EF4;&#x5F62;&#x5F0F;&#xFF0C;&#x4F7F;&#x7528;&#x4E86;&#x53EF;&#x7F29;&#x653E;&#x77E2;&#x91CF;&#x56FE;&#x5F62;&#xFF08;SVG&#xFF09;&#x683C;&#x5F0F;&#x8F93;&#x51FA;&#xFF0C;SVG&#x662F;&#x4E00;&#x4E2A;&#x7528;&#x4E8E;&#x77E2;&#x91CF;&#x7EBF;&#x7ED8;&#x5236;&#x7684;XML&#x6807;&#x51C6;&#x3002;&#x56FE;3.1&#x663E;&#x793A;&#x4E86;sin(r)/r&#x51FD;&#x6570;&#x7684;&#x8F93;&#x51FA;&#x56FE;&#x5F62;&#xFF0C;&#x5176;&#x4E2D;r&#x662F;<code>sqrt(x*x+y*y)</code>&#x3002;</p>
<p><img src="../images/ch3-01.png" alt=""></p>
<p><u><i>gopl.io/ch3/surface</i></u></p>
<pre><code class="lang-Go"><span class="hljs-comment">// Surface computes an SVG rendering of a 3-D surface function.</span>
<span class="hljs-keyword">package</span> main

<span class="hljs-keyword">import</span> (
    <span class="hljs-string">&quot;fmt&quot;</span>
    <span class="hljs-string">&quot;math&quot;</span>
)

<span class="hljs-keyword">const</span> (
    width, height = <span class="hljs-number">600</span>, <span class="hljs-number">320</span>            <span class="hljs-comment">// canvas size in pixels</span>
    cells         = <span class="hljs-number">100</span>                 <span class="hljs-comment">// number of grid cells</span>
    xyrange       = <span class="hljs-number">30.0</span>                <span class="hljs-comment">// axis ranges (-xyrange..+xyrange)</span>
    xyscale       = width / <span class="hljs-number">2</span> / xyrange <span class="hljs-comment">// pixels per x or y unit</span>
    zscale        = height * <span class="hljs-number">0.4</span>        <span class="hljs-comment">// pixels per z unit</span>
    angle         = math.Pi / <span class="hljs-number">6</span>         <span class="hljs-comment">// angle of x, y axes (=30&#xB0;)</span>
)

<span class="hljs-keyword">var</span> sin30, cos30 = math.Sin(angle), math.Cos(angle) <span class="hljs-comment">// sin(30&#xB0;), cos(30&#xB0;)</span>

<span class="hljs-keyword">func</span> main() {
    fmt.Printf(<span class="hljs-string">&quot;&lt;svg xmlns=&apos;http://www.w3.org/2000/svg&apos; &quot;</span>+
        <span class="hljs-string">&quot;style=&apos;stroke: grey; fill: white; stroke-width: 0.7&apos; &quot;</span>+
        <span class="hljs-string">&quot;width=&apos;%d&apos; height=&apos;%d&apos;&gt;&quot;</span>, width, height)
    <span class="hljs-keyword">for</span> i := <span class="hljs-number">0</span>; i &lt; cells; i++ {
        <span class="hljs-keyword">for</span> j := <span class="hljs-number">0</span>; j &lt; cells; j++ {
            ax, ay := corner(i+<span class="hljs-number">1</span>, j)
            bx, by := corner(i, j)
            cx, cy := corner(i, j+<span class="hljs-number">1</span>)
            dx, dy := corner(i+<span class="hljs-number">1</span>, j+<span class="hljs-number">1</span>)
            fmt.Printf(<span class="hljs-string">&quot;&lt;polygon points=&apos;%g,%g %g,%g %g,%g %g,%g&apos;/&gt;\n&quot;</span>,
                ax, ay, bx, by, cx, cy, dx, dy)
        }
    }
    fmt.Println(<span class="hljs-string">&quot;&lt;/svg&gt;&quot;</span>)
}

<span class="hljs-keyword">func</span> corner(i, j <span class="hljs-keyword">int</span>) (<span class="hljs-keyword">float64</span>, <span class="hljs-keyword">float64</span>) {
    <span class="hljs-comment">// Find point (x,y) at corner of cell (i,j).</span>
    x := xyrange * (<span class="hljs-keyword">float64</span>(i)/cells - <span class="hljs-number">0.5</span>)
    y := xyrange * (<span class="hljs-keyword">float64</span>(j)/cells - <span class="hljs-number">0.5</span>)

    <span class="hljs-comment">// Compute surface height z.</span>
    z := f(x, y)

    <span class="hljs-comment">// Project (x,y,z) isometrically onto 2-D SVG canvas (sx,sy).</span>
    sx := width/<span class="hljs-number">2</span> + (x-y)*cos30*xyscale
    sy := height/<span class="hljs-number">2</span> + (x+y)*sin30*xyscale - z*zscale
    <span class="hljs-keyword">return</span> sx, sy
}

<span class="hljs-keyword">func</span> f(x, y <span class="hljs-keyword">float64</span>) <span class="hljs-keyword">float64</span> {
    r := math.Hypot(x, y) <span class="hljs-comment">// distance from (0,0)</span>
    <span class="hljs-keyword">return</span> math.Sin(r) / r
}
</code></pre>
<p>&#x8981;&#x6CE8;&#x610F;&#x7684;&#x662F;corner&#x51FD;&#x6570;&#x8FD4;&#x56DE;&#x4E86;&#x4E24;&#x4E2A;&#x7ED3;&#x679C;&#xFF0C;&#x5206;&#x522B;&#x5BF9;&#x5E94;&#x6BCF;&#x4E2A;&#x7F51;&#x683C;&#x9876;&#x70B9;&#x7684;&#x5750;&#x6807;&#x53C2;&#x6570;&#x3002;</p>
<p>&#x8981;&#x89E3;&#x91CA;&#x8FD9;&#x4E2A;&#x7A0B;&#x5E8F;&#x662F;&#x5982;&#x4F55;&#x5DE5;&#x4F5C;&#x7684;&#x9700;&#x8981;&#x4E00;&#x4E9B;&#x57FA;&#x672C;&#x7684;&#x51E0;&#x4F55;&#x5B66;&#x77E5;&#x8BC6;&#xFF0C;&#x4F46;&#x662F;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x8DF3;&#x8FC7;&#x51E0;&#x4F55;&#x5B66;&#x539F;&#x7406;&#xFF0C;&#x56E0;&#x4E3A;&#x7A0B;&#x5E8F;&#x7684;&#x91CD;&#x70B9;&#x662F;&#x6F14;&#x793A;&#x6D6E;&#x70B9;&#x6570;&#x8FD0;&#x7B97;&#x3002;&#x7A0B;&#x5E8F;&#x7684;&#x672C;&#x8D28;&#x662F;&#x4E09;&#x4E2A;&#x4E0D;&#x540C;&#x7684;&#x5750;&#x6807;&#x7CFB;&#x4E2D;&#x6620;&#x5C04;&#x5173;&#x7CFB;&#xFF0C;&#x5982;&#x56FE;3.2&#x6240;&#x793A;&#x3002;&#x7B2C;&#x4E00;&#x4E2A;&#x662F;100x100&#x7684;&#x4E8C;&#x7EF4;&#x7F51;&#x683C;&#xFF0C;&#x5BF9;&#x5E94;&#x6574;&#x6570;&#x5750;&#x6807;(i,j)&#xFF0C;&#x4ECE;&#x8FDC;&#x5904;&#x7684;(0,0)&#x4F4D;&#x7F6E;&#x5F00;&#x59CB;&#x3002;&#x6211;&#x4EEC;&#x4ECE;&#x8FDC;&#x5904;&#x5411;&#x524D;&#x9762;&#x7ED8;&#x5236;&#xFF0C;&#x56E0;&#x6B64;&#x8FDC;&#x5904;&#x5148;&#x7ED8;&#x5236;&#x7684;&#x591A;&#x8FB9;&#x5F62;&#x6709;&#x53EF;&#x80FD;&#x88AB;&#x524D;&#x9762;&#x540E;&#x7ED8;&#x5236;&#x7684;&#x591A;&#x8FB9;&#x5F62;&#x8986;&#x76D6;&#x3002;</p>
<p>&#x7B2C;&#x4E8C;&#x4E2A;&#x5750;&#x6807;&#x7CFB;&#x662F;&#x4E00;&#x4E2A;&#x4E09;&#x7EF4;&#x7684;&#x7F51;&#x683C;&#x6D6E;&#x70B9;&#x5750;&#x6807;(x,y,z)&#xFF0C;&#x5176;&#x4E2D;x&#x548C;y&#x662F;i&#x548C;j&#x7684;&#x7EBF;&#x6027;&#x51FD;&#x6570;&#xFF0C;&#x901A;&#x8FC7;&#x5E73;&#x79FB;&#x8F6C;&#x6362;&#x4E3A;&#x7F51;&#x683C;&#x5355;&#x5143;&#x7684;&#x4E2D;&#x5FC3;&#xFF0C;&#x7136;&#x540E;&#x7528;xyrange&#x7CFB;&#x6570;&#x7F29;&#x653E;&#x3002;&#x9AD8;&#x5EA6;z&#x662F;&#x51FD;&#x6570;f(x,y)&#x7684;&#x503C;&#x3002;</p>
<p>&#x7B2C;&#x4E09;&#x4E2A;&#x5750;&#x6807;&#x7CFB;&#x662F;&#x4E00;&#x4E2A;&#x4E8C;&#x7EF4;&#x7684;&#x753B;&#x5E03;&#xFF0C;&#x8D77;&#x70B9;(0,0)&#x5728;&#x5DE6;&#x4E0A;&#x89D2;&#x3002;&#x753B;&#x5E03;&#x4E2D;&#x70B9;&#x7684;&#x5750;&#x6807;&#x7528;(sx,sy)&#x8868;&#x793A;&#x3002;&#x6211;&#x4EEC;&#x4F7F;&#x7528;&#x7B49;&#x89D2;&#x6295;&#x5F71;&#x5C06;&#x4E09;&#x7EF4;&#x70B9;(x,y,z)&#x6295;&#x5F71;&#x5230;&#x4E8C;&#x7EF4;&#x7684;&#x753B;&#x5E03;&#x4E2D;&#x3002;</p>
<p><img src="../images/ch3-02.png" alt=""></p>
<p>&#x753B;&#x5E03;&#x4E2D;&#x4ECE;&#x8FDC;&#x5904;&#x5230;&#x53F3;&#x8FB9;&#x7684;&#x70B9;&#x5BF9;&#x5E94;&#x8F83;&#x5927;&#x7684;x&#x503C;&#x548C;&#x8F83;&#x5927;&#x7684;y&#x503C;&#x3002;&#x5E76;&#x4E14;&#x753B;&#x5E03;&#x4E2D;x&#x548C;y&#x503C;&#x8D8A;&#x5927;&#xFF0C;&#x5219;&#x5BF9;&#x5E94;&#x7684;z&#x503C;&#x8D8A;&#x5C0F;&#x3002;x&#x548C;y&#x7684;&#x5782;&#x76F4;&#x548C;&#x6C34;&#x5E73;&#x7F29;&#x653E;&#x7CFB;&#x6570;&#x6765;&#x81EA;30&#x5EA6;&#x89D2;&#x7684;&#x6B63;&#x5F26;&#x548C;&#x4F59;&#x5F26;&#x503C;&#x3002;z&#x7684;&#x7F29;&#x653E;&#x7CFB;&#x6570;0.4&#xFF0C;&#x662F;&#x4E00;&#x4E2A;&#x4EFB;&#x610F;&#x9009;&#x62E9;&#x7684;&#x53C2;&#x6570;&#x3002;</p>
<p>&#x5BF9;&#x4E8E;&#x4E8C;&#x7EF4;&#x7F51;&#x683C;&#x4E2D;&#x7684;&#x6BCF;&#x4E00;&#x4E2A;&#x7F51;&#x683C;&#x5355;&#x5143;&#xFF0C;main&#x51FD;&#x6570;&#x8BA1;&#x7B97;&#x5355;&#x5143;&#x7684;&#x56DB;&#x4E2A;&#x9876;&#x70B9;&#x5728;&#x753B;&#x5E03;&#x4E2D;&#x5BF9;&#x5E94;&#x591A;&#x8FB9;&#x5F62;ABCD&#x7684;&#x9876;&#x70B9;&#xFF0C;&#x5176;&#x4E2D;B&#x5BF9;&#x5E94;(i,j)&#x9876;&#x70B9;&#x4F4D;&#x7F6E;&#xFF0C;A&#x3001;C&#x548C;D&#x662F;&#x5176;&#x5B83;&#x76F8;&#x90BB;&#x7684;&#x9876;&#x70B9;&#xFF0C;&#x7136;&#x540E;&#x8F93;&#x51FA;SVG&#x7684;&#x7ED8;&#x5236;&#x6307;&#x4EE4;&#x3002;</p>
<p><strong>&#x7EC3;&#x4E60; 3.1&#xFF1A;</strong> &#x5982;&#x679C;f&#x51FD;&#x6570;&#x8FD4;&#x56DE;&#x7684;&#x662F;&#x65E0;&#x9650;&#x5236;&#x7684;float64&#x503C;&#xFF0C;&#x90A3;&#x4E48;SVG&#x6587;&#x4EF6;&#x53EF;&#x80FD;&#x8F93;&#x51FA;&#x65E0;&#x6548;&#x7684;<polygon></polygon>&#x591A;&#x8FB9;&#x5F62;&#x5143;&#x7D20;&#xFF08;&#x867D;&#x7136;&#x8BB8;&#x591A;SVG&#x6E32;&#x67D3;&#x5668;&#x4F1A;&#x59A5;&#x5584;&#x5904;&#x7406;&#x8FD9;&#x7C7B;&#x95EE;&#x9898;&#xFF09;&#x3002;&#x4FEE;&#x6539;&#x7A0B;&#x5E8F;&#x8DF3;&#x8FC7;&#x65E0;&#x6548;&#x7684;&#x591A;&#x8FB9;&#x5F62;&#x3002;</p>
<p><strong>&#x7EC3;&#x4E60; 3.2&#xFF1A;</strong> &#x8BD5;&#x9A8C;math&#x5305;&#x4E2D;&#x5176;&#x4ED6;&#x51FD;&#x6570;&#x7684;&#x6E32;&#x67D3;&#x56FE;&#x5F62;&#x3002;&#x4F60;&#x662F;&#x5426;&#x80FD;&#x8F93;&#x51FA;&#x4E00;&#x4E2A;egg box&#x3001;moguls&#x6216;a saddle&#x56FE;&#x6848;?</p>
<p><strong>&#x7EC3;&#x4E60; 3.3&#xFF1A;</strong> &#x6839;&#x636E;&#x9AD8;&#x5EA6;&#x7ED9;&#x6BCF;&#x4E2A;&#x591A;&#x8FB9;&#x5F62;&#x4E0A;&#x8272;&#xFF0C;&#x90A3;&#x6837;&#x5CF0;&#x503C;&#x90E8;&#x5C06;&#x662F;&#x7EA2;&#x8272;&#xFF08;#ff0000&#xFF09;&#xFF0C;&#x8C37;&#x90E8;&#x5C06;&#x662F;&#x84DD;&#x8272;&#xFF08;#0000ff&#xFF09;&#x3002;</p>
<p><strong>&#x7EC3;&#x4E60; 3.4&#xFF1A;</strong> &#x53C2;&#x8003;1.7&#x8282;Lissajous&#x4F8B;&#x5B50;&#x7684;&#x51FD;&#x6570;&#xFF0C;&#x6784;&#x9020;&#x4E00;&#x4E2A;web&#x670D;&#x52A1;&#x5668;&#xFF0C;&#x7528;&#x4E8E;&#x8BA1;&#x7B97;&#x51FD;&#x6570;&#x66F2;&#x9762;&#x7136;&#x540E;&#x8FD4;&#x56DE;SVG&#x6570;&#x636E;&#x7ED9;&#x5BA2;&#x6237;&#x7AEF;&#x3002;&#x670D;&#x52A1;&#x5668;&#x5FC5;&#x987B;&#x8BBE;&#x7F6E;Content-Type&#x5934;&#x90E8;&#xFF1A;</p>
<pre><code class="lang-Go">w.Header().Set(<span class="hljs-string">&quot;Content-Type&quot;</span>, <span class="hljs-string">&quot;image/svg+xml&quot;</span>)
</code></pre>
<p>&#xFF08;&#x8FD9;&#x4E00;&#x6B65;&#x5728;Lissajous&#x4F8B;&#x5B50;&#x4E2D;&#x4E0D;&#x662F;&#x5FC5;&#x987B;&#x7684;&#xFF0C;&#x56E0;&#x4E3A;&#x670D;&#x52A1;&#x5668;&#x4F7F;&#x7528;&#x6807;&#x51C6;&#x7684;PNG&#x56FE;&#x50CF;&#x683C;&#x5F0F;&#xFF0C;&#x53EF;&#x4EE5;&#x6839;&#x636E;&#x524D;&#x9762;&#x7684;512&#x4E2A;&#x5B57;&#x8282;&#x81EA;&#x52A8;&#x8F93;&#x51FA;&#x5BF9;&#x5E94;&#x7684;&#x5934;&#x90E8;&#x3002;&#xFF09;&#x5141;&#x8BB8;&#x5BA2;&#x6237;&#x7AEF;&#x901A;&#x8FC7;HTTP&#x8BF7;&#x6C42;&#x53C2;&#x6570;&#x8BBE;&#x7F6E;&#x9AD8;&#x5EA6;&#x3001;&#x5BBD;&#x5EA6;&#x548C;&#x989C;&#x8272;&#x7B49;&#x53C2;&#x6570;&#x3002;</p>

                                
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